An air data system used in airplanes consists of a pitot static tube or a pressure port in the surface of a fuselage, a pressure sensor measuring a pressure therefrom, and a processor calculating air data from pressure data. In Korea, development of air data probes has been made in accordance with the progress of Korean-model helicopter projects and unmanned aerial vehicle development projects. These pressure measurement-type air data systems have problems such as icing problems in high altitude and low temperature conditions or a decline in the stealth function (increase of radar cross section (RCS)) due to surface protrusion in the case of fighter planes.
Thus, probes are being developed by using an optical method, and optical air data systems (OADS) that are currently under development use a method of using laser Doppler in most cases. In 2003, NATO's Research and Technology Organization (RTO) conducted research into OADS. In 2011, the Netherlands Aerospace Center (NLR) installed an OADS based on Light Detection and Ranging (LiDAR) developed by Thales in the Daniel's project, at an emergency exit of Cessna Citation II and conducted two test flights. NASA has developed a Lidar through Ophir in Colorado as part of its Small Business Innovation Research (SBIR) program. The European Aeronautic Defence and Space Company (EADS) conducted a test flight in 2014 by using a Lidar developed by Optical Air Data Systems, LLC (OADS). Ophir and Japan's JAXA have also completed registration of U.S. patents of LiDAR-based atmospheric data systems in 2005 and 2013, respectively. In addition, Honeywell and Michigan Aerospace have developed their own OADS based on the laser Doppler principle.
A particle image velocimetry (PIV) is a non-contacting velocity measurement apparatus, and has become a state-of-the-art measurement technique to measure a velocity field in the field of fluid measurement in place of a laser Doppler velocimetry (LDV). While it is complicated to install a LDV and the LDV has a disadvantage of point measurement, PIVs have been rapidly spread as they detect a spatial structure of a flow at one time by using a field measurement method and are capable of acquiring accurate velocity information over the entire flow field without disrupting the flow field, and also due to the development of the camera.
Similar to LiDARs, the PIV uses a laser, but uses pulsed light instead of continuous laser light. In addition, since position information of particles is used instead of the Doppler frequency shift of light scattered from particles, the PIV is less restricted by light sources. Also, movement of particles is analyzed by an image processing technique by photographing several particles, and thus, velocity measurement may be performed at a uniform time interval.
FIG. 1 illustrates an example of a particle image velocimetry (PIV) according to the related art.
As illustrated in FIG. 1, the particle image velocimetry according to the related art includes a camera installed in a direction perpendicular to laser light formed as a sheet, and measures two sheets of particles (measurement volume) that pass the laser light sheet within several microseconds, and performs image processing on the sheets to measure a velocity of a flow field.
However, the particle image velocimetry according to the related art requires a special camera and laser, and thus equipment therefor is expensive and difficult to set up. Thus there are many restrictions in using the particle image velocimetry according to the related art. Moreover, the particle image velocimetry according to the related art is used only for setup and it is difficult to use the same as a portable device.